In general, aquatic creatures living under water, such as barnacles, sea squirts, serpula, mytilus galloprovincialis, freshwater shellfish, lagoon bugyul body, visible bluish, greener and so on, adhere to and live in a surface of the body of a ship, which does various damage to the ship.
For example, aquatic creatures adhered to the ship body may increase frictional resistance to seawater, thereby decreasing a sailing speed of the ship and increasing fuel consumption, which is at an economic disadvantage.
Conventionally, a cleaning work by a worker of moving a ship to be cleaned to a land dock and stripping off attachments of the wall of the ship by jetting water with a high pressure hose has been generally used. Since this method requires a preparation procedure to move the ship to the dock, there is a disadvantage that long cleaning time is taken and many workers are mobilized.
A diver may clean the bottom of the ship under water, without moving the ship. However, even for a diver skilled at underwater work environments, it takes a long time to clean a wide range of ship body and the level of difficulty in the cleaning work increases due to poor visibility.
In order to avoid the problem that cleaning the bottom of the ship by a worker is difficult to remove attachments efficiently and requires many workers, there has been proposed a method of applying paints mixed with toxic material in order to prevent marine creatures from adhering and parasitizing in the surface of a ship.
However, the proposed method causes other problems of seawater pollution and detrimental effects on other marine creatures to destroy the aquatic ecosystems and is therefore forbidden by international organizations. In addition, when the toxicity decreases after lapse of certain time, paints should be again applied after cleaning.
In order to overcome such a problem, there has been proposed a technique that a cleaning robot removes deposits while moving along the wall of a ship under water.
“An underwater robot for cleaning and inspection of the bottom of a ship” disclosed in KR Patent Registration No. 10-0811540 is a propulsive apparatus which moves along the wall of a ship body and cleans the wall using a brush fixed at the underwater robot.
However, this method causes upsizing of cleaning equipment due to a propeller, which results in difficulty in efficient cleaning of the ship bottom having a large curvature, and requires many sensors used to stably move the robot along the wall of the ship body, which results in high costs.
In order to clean the bottom of a ship, it is important to closely attach a cleaning apparatus to the ship bottom. To this end, there has been proposed a method of using a magnetic wheel.
FIG. 1 is a schematic view showing a conventional magnetic wheel.
As shown in FIG. 1, the conventional magnetic wheel is used in such a manner that a ferromagnetic circular plate and a magnet are rotated together.
This magnetic wheel is commonly used since a magnetic force, line is concentrated on a ferromagnetic floor when the magnetic wheel is attached to the floor, and its structure is simple.
However, an adsorptive force may be rapidly weakened if there occurs an empty space between any circular plate and the floor.
FIG. 2 is a schematic view showing another conventional magnetic wheel.
The magnetic wheel shown in FIG. 2 maintains an adsorptive force to some degrees even when there occurs an empty space between any circular plate and the floor, unlike the magnetic wheel shown in FIG. 1.
However, this magnetic wheel has poor efficiency since only some of magnets used contact the floor.
In addition, the vicinity of the magnetic wheel is affected since a strong magnetic field ejects to a portion which is in no contact with the ferromagnetic floor. If a worker is present in the vicinity of the magnetic wheel, the worker may be injured due to the magnets.
Further, when the magnetic wheel is rotated, since the magnets are arrange at constant intervals, the adsorptive force to the floor may not be uniformed.
The above description is only provided as a background to assist in understandings of the present invention but is not intended to elucidate the technique known in the art to which the present invention belongs.